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Paddling on Instruments – Part One

In our modern world we are isolated from weather even though we know more
about weather than ever before in human history. We know, for instance, when
a snowstorm is going to drop three feet of new snow in the mountain pass
between here and Seattle; but we will drive to Seattle anyway and do it in a
t-shirt and shorts. This remarkable disconnect between what we know and how
we behave with that knowledge is something that paddlers have to battle with
almost every time we sit our butts down in the cockpit.

Fog and reduced visibility is a fact of life for many paddlers as the
seasons moves inexorably into autumn and winter. The remarkable advances in
clothing have, like your BMW, created a climate control for paddlers most of
us old-timers are not used to. Today we can paddle comfortably in weather
conditions that would have driven all but the craziest of us off the water
ten years ago. Combine this with the simple fact that a lot of paddlers
cannot follow a simple compass course and you could have a recipe for
disaster.

Airplane pilots receive some rudimentary - but mandatory - instructions in
"instrument flying" and navigation while they are training for their pilot
license. Kayakers, if they get any training at all, tend to concentrate on
the technical details of paddling; rolls, braces, paddle strokes, etc. This
is important - and fun - but I think it's also important for paddlers to
learn how to deal with reduced visibility.

The most basic "instrument" on a kayak is a compass. Unfortunately, most of
these compasses are left in the accessory bag in the car and, if they are
not, then they are a temporary ad-hoc addition to the deck. Often secured in
place on a temporary basis with bungee cords with who-knows-what metallic
objects stowed in a hatch right below.

I would like to get one thing straight right off the bat. There are 360
degrees in a circle and your compass will likely divide them up into at
least four 90-degree quadrants of N, E, S and W in addition to the numerical
headings. I say this because you would be surprised at how many people do
not know how many degrees there are in a circle or whether 090 refers to
east (correct) or west (which is 270 degrees).

The first step to understanding the instrumentation on your kayak is
understanding that the "north" on your charts does not - unless you live in
some very specific places - conform to the "north" shown on your compass.
Hence the phrases "true north" and "magnetic north". This difference is
caused by the simple fact that the magnetic pole - the chunk of
whatever-it-is that attracts the needle of your compass - is not directly
under the North Pole but is, instead, displaced some ways away from it. Too
make matters worse, it's on the move.

This is technically called "magnetic declination" but is most often referred
to as "magnetic variation" and unless you live in an area of the world in
which the magnetic north is directly in line with true north then you have
to do an addition or subtraction of the difference before you can correlate
the heading your compass is giving you with the geography presented on your
navigational chart or map.

The term "variation" also refers to some specific magnetic anomalies caused
by changes in the earth's magnetic field in specific areas. These are often
marked on navigational charts and have to be corrected only when your vessel
is in that specific area.

This link (http://www.ngdc.noaa.gov/seg/geomag/declination.shtml) is to the
US NOAA web site explaining more than you need to know about this subject
but also has a link to a map of variation and a calculator for determining
your local variation. I encourage you to click on this link (
http://www.ngdc.noaa.gov/seg/geomag/icons/us_d_contour.jpg) and check the
(2004) magnetic variation for your area. Where I live it was 18 deg east in
2004.

Before we deal with the mechanics of converting magnetic north to true north
(or vice-versa) we need to deal with another correction called "deviation".
And, no, they won't put you in jail for this.

The term "deviation" is used to describe errors in the compass itself and
its close local environment not in the earth's magnetic field the compass is
reacting to. Deviation includes correcting for metalic bits in the vessel
itself as well as to built-in errors in the compass. Some compasses have
adjustments for correcting for deviation (usually small movable magnets in
the base of the compass) but most portable compasses have to be manually
corrected. Compasses for small aircraft have a small placard which says, for
instance, "FOR 090 STEER 096".

Your kayak compass is unlikely to be usefull for heading differences of less
than about 5 degrees simply because the compass card itself is of too small
a diameter to inscribe the degrees and still be legible. In addition, just
the movement of a vessel in a seaway will cause the compass card to swing
wildly back and forth. In addition, changes in speed (acceleration and
deceleration) and rapid changes in heading can create errors. Holding a
compass course can often require that you mentally "average" the compass
readings as you paddle along.

If you have a GPS (and I strongly encourage every kayaker to have a GPS if
only to keep track of your season paddling mileage) correcting for both
variation and deviation is relatively easy. You simply set your GPS to show
magnetic course and paddle a few yards in one direction while comparing the
heading shown on the GPS with that indicated by the compass. The difference
will be deviation (unless you are in an area of significant local variation
differences).

If you do not have a GPS then you have to do some classical marine
navigation. One easy method is to drag your kayak to a place that is marked
on a chart and, from there, use your compass to sight on another place that
is marked on the chart. Use a plotter to determine the true heading between
the two points and the difference between the compass reading and the
plotted (true) heading is a combination of both variation and deviation.
Variation will probably be shown on the chart's compass rose and there is
also often an inner compass circle on the chart which you can use to plot
the magnetic course (remember to compensate for the changes since the chart
was printed). If not you can determine your local variation from that NOAA
link (above. This new difference is entirely deviation so you can begin to
prepare a compass correction card showing what courses to steer for a
correct magnetic course with that compass and that load in your kayak.

The insidious thing about deviation is that, unlike variation, it can change
from one heading to another. It's quite common to have changes of greater
than 10 degrees in a 90 degree course change. So to provide yourself with an
accurate correction card for your particular compass you must, at the very
least, do these procedures for at least 4 different headings about 90
degrees apart.

What happens when you have a temporary mountable compass on your kayak? And
what do you do when you add gear for a camping trip? And just how do you
convert a magnetic course to a true course? That is left for part two. Tune
in for more along with tips on using your GPS on long trips.

Craig Jungers
Royal City, WA